An engine exhaust system typically includes catalytic converters in downstream fluid communication with exhaust manifolds to reduce pollutants from engine exhaust gases. Catalytic converter temperature is often used as an input variable to control engine operation and for government regulated On-Board Diagnostics (OBD). OBD measures include monitoring engine exhaust systems for various conditions that may cause undesirable increases in pollutant emissions.
One OBD measure involves periodic testing of oxygen (O2) sensors in the exhaust system. The O2 sensors are tested as a function of catalytic converter temperature, which is typically estimated. Such temperatures may not be reliably estimated for certain engine configurations such as variable displacement V-6 engines wherein an entire cylinder bank may be periodically deactivated and reactivated to conserve fuel. Exhaust gas temperatures from such a bank fluctuate greatly and existing temperature models may not reliably estimate temperatures of a catalytic converter downstream of such a cylinder bank.